This invention relates generally to optical systems and more particularly, to methods and apparatus for measuring a surface contour of an object.
Accurately measuring a contoured surface of an object may be a significant factor in determining a manufacturing time of the object, as well as a factor used to determine subsequent maintenance and repair costs and activities. More specifically, when the object is a gas turbine engine blade airfoil, or an airfoil forging die, accurately measuring the contour of the blade airfoil, or the forging die, may be one of the most significant factors affecting an overall cost of fabrication of the gas turbine engine, as well as subsequent modifications, repairs, and inspections of the blade airfoils.
Conventional inspection methods include using a plastic template that fits over the blade to enable comparisons to be performed between the blade and dimensions indicated on the template. However, because of the contour of the blade airfoils, fabricating such templates may be a costly and time-consuming process. Furthermore, obtaining accurate comparisons between the template and the blade at the various orientations of the blade airfoil may also be a difficult task.
To facilitate more accurate shape and orientation verifications, at least some known inspection methods include guillotine gauges and/or coordinate measuring machines (CMM). Guillotine gauges are expensive and require a high degree of operator skill and interaction with the gauging process. More specifically, to accurately use a guillotine gauge, a plurality of accurate measurements must be obtained using feeler gauges and/or calipers. However, such verification techniques may be time intensive as they may require manual recording of measurements.
CMMs have also been used to obtain dimensional information of an object. Within such systems, a probe is positioned within a three-coordinate measurement space to contact an object surface, at which time the position of the probe tip is measured. The process is repeated many times to determine a surface contour. CMMs are expensive and such a verification process may be time-consuming to accurately map the surface profile and location of an blade airfoil. Furthermore, within at least some known CMMs, an accuracy of the CMM may degrade when measuring surface contours having a small radius, such as the leading and trailing edges of an blade airfoil.